Form stable coreless packages of foamed thermoplastic twine and processes of manufacture



INVENTOR. H A HOOD m, .bfi

H. A. HOOD TWINE AND PROCESSES OF MANUFACTURE Filed 001,. 28, 1965 FORMSTABLE CORELESS PACKAGES OF FOAMED THERMOPLASTIC Nov. 26, 1968 A TTORNE' V5 United States Patent O 3,412,954 FORM STABLE CORELlESSPACKAGES OF FOAMED THERMOPLASTIC TWINE AND PROCESSES OF MANUEACTUREHenry Alexander Hood, Moorestown, NJ., assignor to Wall Industries,Inc., a corporation of Delaware Filed Oct. 28, 1965, Ser. No. 505,467 9Claims. (Cl. 242-159) ABSTRACT OF THE DISCLOSURE Foamed thermoplastictwine is either Iheated to a temperature in the range of 100 F. to 185F. below the melting point thereof and immediately wound on a core, orwound on the core and then heated to such temperature. After cooling,the core is removed to provide a form stable coreless package of twine.

This invention relates to improved foamed thermoplastic twine andcoreless packages thereof.

The well-known advantages of cords, yarns and twines formed ofthermoplastics make them acceptable for many potential uses. Such yarnsand twines are generally light weight, inert against rotting anddeterioration due to many chemicals, do not absorb water, have littlestretch and have a high tensile strength. Many potential uses ofsynthetic fibres and twines require a package of the twine that iscoreless and form stable, such as for use in baling machines. Synthetictwines exhibit a degree of livelness or tendency to untwist and slipagainst themselves which frequently causes coreless packages of thetwines to telescope and/ or become uneven and unfit for use in manyapplications.

Accordingly, typical objects of this invention are to provide:

(l) Improved foamed thermoplastic twine;

(2) Form stable coreless packages of thermoplastic twine; and

(3) An improved method for producing form stable coreless packages ofthermoplastic twine.

Other objects, aspects and advantages of this invention will becomeapparent to one skilled in the art upon further study of this disclosureand the appended claims.

It -has been determined that if foamed synthetic monoiilaments are used,at least in part, to form twines, the resulting twine exhibits lessslippage, improved knotting and lighter weight than synthetic twinespreviously available.

Broadly, in accordance with this invention, foamed synthetic twines areheat treated to set the twine in position as wound into a package.Preferably, the twine is heated just prior to being wound onto a coreand then cooled while on the core with the core being removed at theconclusion of the cooling. However, satisfactory heat setting can beobtained by heating and cooling the wound package of twine while on acore. After cooling and the twine is set, the core is removed, leaving aform stable coreless package of twine.

In the drawings, FIGURE l is a diagrammatic representation of a processin accordance with one embodiment of the invention, FIGURE 2 is adiagrammatic representation of a process in accordance with anotherembodiment of the invention, and FIGURE 3 is an elevational View, partlyin cross-section, of a form stable coreless package of twine produced byeither the process of FIG- URE 1 or the process of FIGURE 2.

The twines applicable to this invention may comprise a single strand ora plurality of strands. The single strand twine is formed by twisting aplurality of foamed mono- CII rice

filaments together and the multi-strand twine is formed by twisting twolore more strands, each comprising a plurality of foamed monofilaments,together in the direction opposite to that of the individual strands. Inthe multi-strand twines, all or a portion of the strands may have thesame number of turns per inch or they all may have a different twistratio.

This invention is applicable to foamed twines formed from any syntheticmaterial capable of being formed into monolaments and which are formsettable by heating and cooling. At present, satisfactory twines arereadily made from olen polymers which include yhomopolymers andcopolymers formed by polymerizing olens having 2 to 8 carbon atoms permolecule such as polyethylene, polypropylene, ethylene-butene-lcopolymer, poly-l-butene, poly-2-methy1 pentene, polyisobutylene, andthe like. The polymers used for the twine applicable to this inventioncan contain stress cracking and oxidation inhibitors, vulcanizatiouinhibitors, llers, pigments, and the like. The applicable polymers canbe produced by any suitable process. The polymerization processdescribed and claimed by Hogan et al. in U.S. 2,825,721 (1958) producespolymers very acceptable for the fabrication of monolaments and twines.

Various gaseous, liquid and solid foaming agents can be utilized toproduce the foamed monoilaments. In general, these agents comprisematerials which are gaseous at the temperatures of the molten plastic orpolymer at the extrusion die. Solid materials which decompose at thesetemperatures and yield gaseous products tor components which react withother ingredients present in the melt to produce gaseous products areapplicable. Any inert gas which is nondeleterious to the polymer orplastic being extruded is feasible. Such gases include N2, steam, CO2,low boiling hydrocarbons (propane, bfutane, pentane), and Freon. Liquidsinclude water, ammonia, and hydrocarbons which vaporize at the extrusiontemperatures as pressure outside of the die is released. Solid materialsinclude p,poxybis(benzenesulfonyl hydrazide) which is sold under thetrade name of Celogeu by Naugatuck Chemical, a division of the UnitedStates Rubber Company; l,1-azo-bisformamide, diazoaminobenzene,dinitrosopentamethylenetetramine, 4-nitrobenzene sulfonic acidhydrazide, beta-naphthalene sulfonic acid hydrazide, diphenyl-4,4di(sulfonyl azide), and mixtures of materials such as sodium bicarbonatewith a solid acid such as tartaric acid. The amount of foaming agent canbe any suitable value, and is usually in the range of 0.01 to 50 weightpercent of the polymer being processed, with the preferred range beingfrom 1 to l5 weight percent.

The temperature employed for the heat treatment required in thisinvention will vary depending upon the filament and twine diameters andthe type of polymer used to form the twine. The temperature to which thetwine is heated will be below the melting point thereof and generallywill be within a range of to 185 F. below the melting point of thepolymer. For the higher melting point polymers, such as polypropylene,the twine temperature of treatment generally will be between and F. withthe preferred value being approximately half that of the melting pointof the polymer measured in F.

When heating the wound package to set the twine in place, the heatingrate can vary from l0 to 30 F. per hour. Heating rates :higher than 30F. per hour cause distortion of the package due to differentialshrinkage and shortening of the outer layers due to a temperaturedifferential from the outside to the inside of the package. The extendediheating periods required by heating rate less than 10 F. Iper hour tendto deteriorate the polymer. Generally, the twine will be maintainedunder a tension of: 1 to 10 pounds during winding to obtain a tightuniform packing.

The following examples will illustrate the lpresent invention in greaterdetail, but are not intended to be construed as limiting the invention.

Example I Polypropylene having a density of 0.91 grams/ cc. asdetermined by ASTM D1505-63T is blended with 0.22 weight percent of1,1azobisf0rmamide, a blowing agent and the blend is extruded into 5 80denier foamed monoiilaments. Forty of these monolaments are twistedtogether with a Z twist of 12 turns per foot to form baler twine. Suchtwine possesses superior knot retention characteristics as compared tobaler twine made from nonfoamed monofilaments. These superiorcharacteristics improve the use of synthetic twines in the farmingindustry (baling machines) and also for general industrial use.

Example II Polypropylene twine as prepared in Example I is passedthrough a radiant heating zone and the twine is heated to about 160 F.The heated twine is immediately wound onto a tapered core being lOl/2inches long and tapering in diameter from 2% inches at one end to 2%.inches at the opposite end under a tension of from about l to aboutpounds and at a rate of 450 feet per minute until the spool of twine isabout 9 inches in diameter and 917/2 inches long. The resulting spool isallowed to cool to ambient room temperature air for 5 hours and the coreis then removed with ease. After storage of the coreless package at roomtemperature for one day, no significant telescoping of the twine occursand the package of twine is completely satisfactory for use in balingmachines, Further, after storage of the heat treated coreless packageformed in this example at 130 F. for 16 hours, the package issatisfactory and had not telescoped.

Example III Polypropylene twine as prepared in Example I is passedthrough a radiant heating zone and the twine is heated to about 160 F.The heated twine is immediately Wound onto a tapered core being lOl/2inches long and tapering in diameter from 21A inches at one end to 2%inches at the opposite end under a tension of from about l to about 10pounds and at a rate of 450 feet per minute until the spool of twine isabout 9 inches in diameter and 91/2 inches long. The core is removedfrom the spool immediately and the resulting spool is allowed to cool toambient room temperature air for 5 hours. After storage of the corelesspackage at room temperature for one day, the center portion of thepackage has telescoped out the end about 1/2 inch and the inner windingsare axially displaced relative to the outer winding. The package oftwine is unsatisfactory for use in baling machines.

Example IV Polypropylene twine as prepared in Example I is wound onto atapered core being 101,42 inches long and tapering in diameter from 21Ainches at one end to 2% inches at the other end under a tension fromabout 1 to about 10 pounds at a rate of about 450 feet per minute untilthe spool of twine is 9 inches in diameter and 91/2 inches long. Thecore is then immediately removed and the coreless package of twine isstored at room temperature. Inspection of the package after one dayshows the center portion of the package is telescoping out the end about1/2 inch and the inner windings are axially displaced relative to theouter winding. The package is completely unsatisfactory for future usein baler equipment.

Example V Polypropylene twine as prepared in Example I is wound onto atapered core being 101/2 inches long and tapering in diameter from 2%,inches at one end to 2% inches at the other end under a tension fromabout 1 to about 10 pounds at a rate of about 450 feet per minute untilthe spool of twine is 9 inches in diameter and 91/2 inches long. Thepackage of twine is stored at room temperature. After 5 hours of storagethe core is removed with great difficulty. Inspection of the packageafter one day of storage shows the center portion of the package istelescoping out the end about 1/2 inch and the inner windings areaxially displaced relative to the outer winding. The package iscompletely unsatisfactory for future use in baler equipment.

Example VI A package of polypropylene twine as formed in Example IV withthe core removed and at a temperature of about F. is heated in aconvective oven for 4 hours and l5 minutes at which time the temperatureof the twine reaches 160 F. After cooling, removal of the core, andstorage for one day, the coreless package of twine does not exhibit anytelescoping and is a form-stable package of synthetic twine satisfactoryfor many uses.

Example VII A package of polypropylene twine as formed in Example IVwith the core therein and at a temperature of about 80 F. is heated in aconvective oven for 4 hours and 15 minutes at which time the temperatureof the twine reaches 160 F. The core is removed immediately after thepackage leaves the oven, and the package is allowed to cool. Aftercooling and storage for l day, the coreless package of twine exhibitstelescoping and is unsatisfactory for many uses.

Example VIII A package of polypropylene twine as formed in EX- ample IVwith the core therein and at a temperature of about 80 F. is heated in aconvective oven for 4 hours and 15 minutes at which time the temperatureof the twine reaches 160 F. After cooling and storage for one day, thecoreless package of twine is misshapen and unsatisfactory for many uses.

From these examples it is seen that the problem of telescoping ofcoreless packages of synthetic twine is eliminated by the practice ofthis invention.

To one skilled in the art it will be apparent that many variations andmodifications of this invention can be practiced in view of theforegoing disclosure without departing from the spirit and scopethereof. For instance, another heating means that may be used forheating the strand or wound package is frictional heating. This may beaccomplished by sliding the surface of the strand over another surfaceso as to induce frictional heat on the strand surface or it may be byflexing or twisting of the strand so as to induce relative movementbetween the contacting monotilaments making up the strand therebyinducing frictional heat. Ultrasonics may also be used to induce heatingwithin the strand or wound package. Other forms of inducing heating suchas dielectric heating, if the strand is non-conductive, and inductiveheating, if the strand is electrically conductive, may also be used.Also, it will be apparent that many of the variables employed in theexamples will vary depending upon the synthetic material and physicalproperties of the twine and package.

I claim:

1. A method of providing a form stable coreless package of twine formedof a foamed thermoplastic material capable of being form set by heatingand cooling, comprising heating the foamed thermoplastic twine to atemperautre in the range -of F. to 185 F. below the melting point ofsaid thermoplastic material, substantially immediately winding the thusheated twine onto a core to form a package, cooling said heated twineWhile Wound on said core, and removing said core from the resultingcooled twine.

2. A method in accordance with claim 1 wherein said thermoplasticmaterial is polypropylene.

3. A method in accordance with claim 2 wherein the temperature to whichthe twine is heated is in the range of 160 F. to 195 F.

4. A form stable coreless package of foarned thermoplastic twineprepared in accordance with the method of claim 1.

5. A method of providing a form stable coreless package of twine formedof a oamed thermoplastic material capable of being form set by heatingand cooling, comprising Winding the foamed thermoplastic twine on a coreto form -a package, heating the package to a temperature in the range of100 F. to 185 F. below the melting point of said thermoplastic materialat a rate of from 10 F. to 30 F. per hour, allowing the temperature ofthe thus `heated package to lower to room temperature, and removing thecore from the thus cooled package.

6. A method in accordance with claim 5 wherein said twine is wound ontosaid core under a tension of 1 to 10 pounds.

7. A method in accordance with claim 6 wherein said thermoplasticmaterial is polypropylene.

8. A method in accordance with claim 7 wherein the temperature to whichsaid package is heated is in the range of 160 F. to 195 F.

9. A form stable coreless package of oamed thermoplastic twine preparedin accordance with the method of claim 5.

References Cited UNITED STATES PATENTS 2,425,060 7/ 1943 Ingersoll.

3,046,632 7/ 1962 Tsutsumi 28-62 XR 3,118,161 1/1964 Cramton.

3,256,258 6/1966 Herrman.

3,262,257 7/1966 Martin.

FOREIGN PATENTS 39-7262 5/1964 Japan.

JULIUS FROME, Primary Examiner.

PHILIP E. ANDERSON, Assistant Examiner.

